There has been an assumption that your mother HAS separate holiday insurance. If it is ruled the driver's fault, his insurance certainly should cover her treatment, and possibly the upgraded plane fare. If your mother does have holiday insurance, she should submit everything there, and the insurance companies ought to fight it out. She should be reimbursed through her policy, and they should deal with the driver's company.
If it hasn't been done, I would have your mother write down what happened in her own summary and make sketches (photos would be ideal) of the location and what occured while it is still relatively fresh in memory. Date any documents like that. It can never hurt, especially if one needed to challenge a ruling.
For any bills that arrive, get documentation proving the expense was medically necessary. For example, if you can get a doctor to state in writing that she needed more space on the plane, do it! It may be "obvious", but documentation is best, and could indeed be required.
If her only coverage is through Medicare, contact them to see what they might cover (
www.medicare.gov). I suspect it is limited outside the US, but may at least cover some emergency care.
Good luck and a speedy recovery to your mother!